


Infinite Square Well Potential

by Spurge_Laurel



Category: The Adventures of Jimmy Neutron: Boy Genius
Genre: Aged-Up Character(s), Comedy, Consensual Sex, F/M, Grown up Cindy Vortex, Grown up Jimmy Neutron, Maybe - Freeform, Romance, Romantic Comedy, Sex, Tsundere Cindy Vortex, Vaginal Fingering, Vaginal Sex, again maybe, not really - Freeform
Language: English
Status: Completed
Published: 2021-01-28
Updated: 2021-01-28
Packaged: 2021-03-13 19:15:25
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,846
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29033766
Author URL: https://archiveofourown.org/users/Spurge_Laurel/pseuds/Spurge_Laurel
Summary: Now in college, Jimmy and Cindy have an arrangement for when they’re both back in Retroville to visit their families during the holidays. It’s not perfect, but it’s them. Smut.
Relationships: Jimmy Neutron/Cindy Vortex
Comments: 1
Kudos: 6





	Infinite Square Well Potential

**Author's Note:**

> A wild Jimmy Neutron fic appears, do you a) fap, b) question your life decisions that lead you here, c) ignore, or d) question my sanity. All jokes aside, this is a super random story that no one asked for or wants. I wanted to do something fluffy and wholesome, but it didn’t super work. There’s some sex and some emotional stuff and also a bit of comedy that isn’t really funny.

Cindy climbed the stairs of her parents house, heading back to her old room, her slender hand encapsulated in James Neutron’s now larger one. She remembered back in elementary school when he was just a little munchkin. Whatever happened to that cute little Jimmy with his oversized head? Now it was too tall James with his lanky arms. And his stupid soft serve hair style never changed, either, giving him another foot. It wasn’t fair that once he started he just kept growing and growing while she capped at an even five feet. 

Dammit, being in this stupid house again was making her reminisce. Why the hell would she do that? The past was pretty shitty, and the stupid act she would put on to try and deal with it made her wince. The only good part of her childhood was the dumb lug she was draggin into her childhood bedroom. Well, maybe not only the good part, but definitely the thing that made it bearable. 

“Oy,” Cindy felt a finger poke her shoulder and turned to look. James was giving her that smile again. The soft one, filled with warm contentment that never failed to spark a fire inside her when it was directed her way. “Stop that, I can see the storm clouds gathering. Didn’t we agree on only happy thoughts?”

Cindy quickly looked away and down, flushed but trying to hide it. She knew James knew that she knew that he knew exactly how red her face was, but he let her have her moment. She couldn’t understand how he could always cut right to her core like that. Here they were, in her parents’ house, in her old bedroom, about to have sex at her discretion, yet he could still have her blushing like a schoolgirl with ease. She really hated the nerd. And she hated how she couldn’t hate him.

“Start stripping, doofus,” she said, still not looking at him while beginning to take her clothes off. Her t-shirt was quickly pulled over her head and discarded, exposing her purple bra clad B-cups. Without even waiting she moved on to her pants, unbuttoning her jeans and sending them to her ankles before kicking them away. Left in only her matching bra and panties, Cindy looked over to see James unbuttoning the last button on his shirt.

“Have you been working out?” she asked, unable to help herself. His abs looked really good. He definitely didn’t have those last time she’d seen him. “Whatever you’ve been doing, it’s definitely working.” The blonde gently reached out to feel up his torso, impressed against her will by how firm he felt now.

“Careful there, if you keep complimenting me, my already big head will grow even bigger,” James waggled his eyebrows, obviously not talking about his actual head. “Then I might have trouble fitting it in your small room.”

Cindy smacked his pecs with the back of her hand, but she was smiling. “Damn, Nerdtron, when did you become sauve? What happened to King Dweebus?”

“He had to grow up and make some new friends.”

That kind of brought the mood down. Cindy pulled back, looking down once more. “It’s not our fault, you know?” she said, her voice small. Hurt. “That you outgrew us, I mean. It’s you who’s the problem. You’re a weird freak of nature.”

Long arms packed with surprisingly powerful muscles wrapped around her in a tight embrace, James resting his chin on the top of her head in a way she absolutely hated and in no way at all liked even a little bit. “That’s not what I meant, Cindy. You’re always doing this, twisting my words around.

“I didn’t outgrow you guys or leave you behind or anything. Especially not you, Ms. Vortex, you could always give me a run for my money, even if you don’t accept it anymore. But everyone’s moving in their own direction nowadays, exploring things that make them happy and figuring out just who they want to be. I don’t think that’s a bad thing, that’s just part of growing up. And at the end of the day we’ll always meet back here in Retroville.”

Cindy could feel her body sink into James’s hug, but her mind still raced. It was a good speech, but it just didn’t ring true to her. She certainly didn’t feel like happy when she studied law, and though her family pushed her to be a lawyer she had no real interest in that career. Honestly, she didn’t have much interest in much of anything anymore. Life kind of passed her by in a haze and nothing she did seemed to have any effect. The only light she had left was her infrequent meetings with James during the holidays.

Finally, she got tired of waiting. “Stop teasing me,” she said, pushing him away and climbing onto the bed. “You’re still almost fully dressed and I’m nowhere near that promised orgasm so powerful I would forget all about the disaster that was this year’s Christmas party.”

James chuckled but acquiesced, removing his pants. He joined her on the bed, and the two rivals turned lovers fell into a practiced make out session. Their hands roamed without restriction, caressing each other’s body and discovering all the changes since their last time together. And Cindy had so much to discover. Namely, all the new muscles that found their way onto her once scrawny and noodle armed friend. Oh, she could definitely still kick his ass six ways to Sunday, but it was almost nice to imagine him keeping her safe in his strong arms.

Meanwhile, James had found something too. “Have you breasts finally grown?” he asked, cupping said boobs over her bra. “They feel a bit fuller then I remember.”

“Jerk. I’ll have you know my breasts are a perfectly good size. They are noticeable without being a distraction, and not so big that my back suffers. Big breasts would get in the way when I do Judo, anyways, so it’s actually better that they’re like this. Also, they’re actually bigger than they seem because my pecs-”

James stopped her rant with a kiss. “I’ll have you know,” he whispered, his breath heating up her face, “that I like them small. More than a handful is a waste, as they say.”

“Creep,” Cindy mumbled, but she let him kiss her again and take off her bra without complaint. The purple garment went flying into a corner of the room to be forgotten until tomorrow. James wasted no time moving his mouth to one of her nipples, giving the pink nub a tender lick. Cindy’s sharp inhale emboldened him, causing him to close his lips around the sensitive flesh. Her hands came up to his head and buried themselves in his hair, her fingers tangling in his brown locks to pull him deeper into her chest. She could feel him smile against her skin, but she let him have his fun.

Still, Cindy had never been known for her patience, and the foreplay was making her figuratively itch with anticipation. When James finally pulled back from her breast she was excited to finally get to the action, but instead he simply moved his head to the other one. Some of her disappointment must have shown on her face because he satisfied himself with just a little nibble before moving up to kiss her deeply.

“Sorry,” he said, “but it wouldn’t be fair to pay attention to only one of your girls. Then the other might start to feel left out, and we wouldn’t want that.”

“Corny dork, just fuck me already.”

The two quickly removed their last pieces of clothing and fit a condom on James’s penis before resuming their position on the bed, with him on top of Cindy. With one hand, he lined himself up, but before he went through with the penetration he caught her eyes. “Are you sure?” He asked, entirely serious for the first time tonight.

Cindy groaned and rolled her eyes. “You ask me that every time we have sex, James. Just stick it in already, you big dolt.”

“Hey, I’m just making sure. Getting consent is important, you know. Just because you’ve wanted it before doesn’t mean you want it now.”

As an answer, Cindy grabbed James’s hand and pressed it against her entrance. “Do you feel that?” she asked, pushing one of his fingers inside. “Do you feel how wet I am? It seems pretty obvious to me whether or not I want it.”

“A physiological reaction is not a proper indication of desire, Cindy,” he lectured, but he continued to finger her as he spoke, slowly stretching her out and preparing her for what was to come. “Consent sounds like an enthusiastic yes, and I’m not hearing much enthusiasm from you. Maybe you don’t want this after all.” As if to stress his point, he slowly started to pull his finger out, but curling it so that it dragged on her walls so exquisitely.

“Okay, fine! I want you, okay! I really want you! It’s been so fucking long and I’m so fucking pent up and I just need a-AAAAAAH!”

Cindy was cut off by her own pleasured moan as James sunk all the way into her with one, solid motion. His much taller frame crowded her from all sides, and all she could see was his strong arms holding him up above her, his chiseled torso with rippling muscles, and his handsome face top with a swirl of brown hair. And the way he was grinning down at her, Cindy felt her heart flutter. And in some dark recess of her brain, a realization occurred. Maybe on-again-off-again, friends-with-benefits, basically lovers but not really relationship wasn’t quite what she wanted with James. 

“What are you thinking in that pretty little head of yours?”

“I’m sorry we can’t all have freakishly big brains, King Cranium.” But she wasn’t ready. Not for. . . love, if that really was what she was feeling. That was why she had broken things with him in the first place. “I was just wondering how you could stand to have such a hot piece of ass all but begging for you and yet not fuck her brains out.”

“Are you trying to tease me? Actually, that begging thing sounds good. How about you do that? Maybe then I’ll start moving.”

“I don’t know why I even brought you over. Clearly your head is so big to overcompensate. I mean, I can barely even feel you inside of me,” it was a lie and they both knew it. James wasn’t massive by any stretch, but he was larger than average, and Cindy had a kind of tightness achievable by fucking only one person every few months. “Maybe you should just leave. I’ve got a vibrator in my drawers that could do a better job pleasuring me, and then there is no chance of your ugly mug spoiling the mood right as I’m about to cum.” 

James wasn’t cracking, still just holding himself above her, his cock stuffed to the balls in her vaigna but stationary. Cindy was getting a bit desperate, her hips rolling slightly by themselves to try and eek out some friction, but the genius was having none of it. He sat back so that he was resting more on his legs and grabbed her hips, forcing her to be still.

“Urgh! You really want me to beg? Well, alright! I’m begging you to get off your lazy ass and go to your lab so that you whip up some formula to make you into less of a useless manchild who can’t even fuck properly! Then it will invariably go horribly wrong and I’ll have to come to your rescue like always without even getting anything out of it because you’ll transform back into this worthless buffoon that just sits there when he could be fucking the hottest girl in this two-bit town!”

“Blonde girl make Jimmy so angry!” James cavemanned with a mischievous grin showing he wasn’t really angry. However, something she said must have gotten to him, because he did begin to forcefully thrust into her, “Jimmy smash blonde girl!”

“Gah! Yes! Like that! Just like that!”

“You like this, do you?” James placed his hands back on her breasts, kneading the small mounds in time with his motions. Cindy’s limbs came up to wrap around him, pulling him in closer. Her legs locked behind his ass while her hands clutched at his back, her nails making red ridges in his skin. “You’ve never been like this before,” he noted.

“It’s-Ah-your muscles! Oooh! They really-Oh, yeah, right there!-really turn me on!”

“I’m glad,” his thrusts started picking up speed, his words broken up by huffs, “I did get them for you. Guess now I have some motivation to keep them.”

“YES! Oh, god yes! You’re so hot!”

“I’m getting close.”

“Me, too. I’m gonna cum. You’re gonna make me cum. I’m gonna. . . gonna. . . gonna-”

James hilted himself, “I’m cumming!”

“-CUM!”

Mid orgasm, James moved to kiss Cindy, and she instantly responded. Thought it was less of a kiss and more of mashing their lips together in an unsynchronized and sloppy mess. As they came down from their highs, it transformed into a proper kiss, before degenerating into a passionate make out session. Finally James had to pull back for air, his brow dripping with sweat. Cindy scrunched her brow when a drop landed on her face, making James laugh before he rolled off her.

The two lay side by side in their afterglow, just enjoying each other’s presence in silence, staring at the ceiling. Then Jimmy rolled over to face the feisty blonde. “Have I ever told you about the time I visited the future?”

Cindy pushed herself up to her elbows, eyebrows raised in curiosity. “No, I’ve never heard this story,” she said, “when did it happen? Why wasn’t I there?”

“This was from before you really joined our little group. You remember Libby’s birthday party? The one where she went mad with power?”

“Uh, no? That happened?”

“Oh, right, timeline correction. Of course you wouldn’t remember.”

“James Isaac Neutron, what have you been doing to the time stream?”

“Nothing you need to worry your pretty little head over. Don’t you want to know about the future, though?”

“I don’t know, isn’t that dangerous?”

“I won’t tell you anything big, don’t worry. Just some fun stuff, like how Sheen becomes a model.”

“Sheen? A model? No way! Now I know you’re messing with me!”

“No goofs, it’s true! And Carl runs a llama sanctuary where he teaches them to talk in English.”

“And let me guess, you win every Nobel Prize there is, huh?”

“Yeah, exactly, how’d you know?”

“Oh, please, Nerdtron, as if I haven’t been in the gravitational well of your ego before. It doesn’t take a genius to figure out your little fantasy.”

“Hehe, I guess you have a point, the future does sound a bit like a wish fulfillment dream. But that was only the good timeline, we didn’t actually go there, only watched it through the portal. The future we actually went to was terrible.”

“Then why’d you go there?” 

“Didn’t have a choice. There was an. . . incident with Libby’s gift and she may have gotten an experimental chemical I was working on that increases dominant urges and encourages tyrannical behavior in people. She completely took over Retroville and turned it into her own autocratic state. Giant killer police robots and everything.”

“That sounds horrible!”

“Oh, it was. In that timeline, Carl was actually a wanted criminal and on the run, if you can believe it?”

“I really can’t. What was his crime?”

“Something stupid like not dancing or wearing the weird outfits everyone else did. I don’t really remember. It didn’t seem important at the time, what with the aforementioned giant killer police robots on our tail and everything.”

“Well, I guess I’m just glad that you managed to fix your fuck up. I don’t think I’d like to live in such a world.”

“Believe me, you wouldn’t. And I hadn’t even gotten to the worst part.”

“It gets worse?”

“Six orders of magnitude worse. The absolute most horrible, terrible, insidious, dastardly, down right demonic thing in that cursed timeline Carl, Sheen, and I were almost murdered in had to be my own fate.”

“What, were you like a slave or something? Forced to make those police robots in a dark dungeon somewhere?”

“Even worse. I was married to you.”

Cindy took two seconds to process exactly what James had just said, before erupting in furious blush. Furious indeed, for she immediately kicked him out of her bed at full strength. He fell crashing to the floor, laughing all the while. But Cindy wasn’t really mad, she knew he was just teasing. And maybe, somewhere deep down, like really deep down, some itty bitty tiny part of her had the thought, perhaps that wouldn’t be so bad after all.

**Author's Note:**

> Sorry if this was kind of shit. I tried, but it’s hard to write smart characters when you’re so dumb. Don’t ask me how I got my job, I’m still wondering that to this day. Anyways, this is the first of the promised quick writes. Next will either be another quick write or another chapter of Perfect Wife.


End file.
